1. Field of the Invention
The present invention relates to the field of oil field drilling equipment, especially to blowout preventors.
2. Description of the Prior Art
Blowout preventors are necessary to protect the drilling rig, the workers and the environment from possible blowout conditions.
There are two main types of blowout preventors (BOP's), annular and ram. Such BOP's are typically mounted in the wellhead such that the drill pipe extending from the derrick to the bottom of the bore hole also extends through the BOP. Ram type preventors seal the bore by forming a top seal between the movable ram and the BOP housing and a face seal between opposing rams or opposing rams and the intervening drill pipe. The seals are made of a thick rubber capable of handling the required pressures. Today, such seals typically include a face seal section joined with a semi-circular peripheral section known as the top seal. A top seal is used because the high pressure fluids are coming up the well bore and therefore force the rams upward.
It is necessary for the top and face seals to provide a continuous seal around the entire ram and for the seals to be firmly attached to each ram block. In use, it is known that the resilient seals wear out and must be removed from the BOP rams and replaced. In one prior art ram seal the face seal was first inserted into the face of the ram. The top seal was then placed into a groove formed in top of the ram. The two seals were held in place by pins extending from the top seal which mated with face seal and resulted in a locking configuration. This ram seal design had the problem that it would not function if installed upside down because there was only one top seal.
This problem of upside down installation was addressed in another prior art design as illustrated in U.S. Pat. No. 3,434,729. In this design a single piece ram seal was developed that was symmetrical. A ram block floated in the ram, with the top seal being affected by the well pressure. The ram block was essentially a semicircular cylindrical section, with the ram seal surrounding the perimeter of the ram block. The portion of the ram seal that contacted the circular portion of the block formed the top seal and was split horizontally. This design allowed the ram block to be inserted into the single piece seal by separating the top seal horizontal portions and sliding the ram block through the upper and lower horizontal portions of the ram seal until the ram block contacted the face portion of the seal. The ram seal was held in place on the ram block by the use of two retaining screws mounted through the ram block and mating with trunnion nuts located inside the face portion of the seal. This ram seal design did overcome the upside down problem, but the seal was difficult to install on the ram block because of the thickness and strength of the materials involved. This ram seal also had the problem that both the top and the face seals had to be replaced together. Because the face seal generally wears out much faster than the top seal, top seals having significant usable life were being discarded, increasing the cost of operation.